As Spica said, it was the educational version of Celestia which had a lot of those nice extras. Others are available as standalone addons from the Motherlode. There was nothing really "amazing" about how nice everything looked, nothing more than what we all know about Celestia; it is all smoke and mirrors and very good work by addon creators to make it all look so nice.

(SpaceEngineer)

Are there procedural planets introduced?

No. Procedural generation was never implemented in Celestia, and it was never even a priority for the dev team.

No. Procedural generation was never implemented in Celestia, and it was never even a priority for the dev team.

However, globular clusters have a model with procedually (or randomly?) generated "stars". They not are start actually, just sprites, you can't click on a "star" and fly to it. So they starting to use some procedural generation though.

"Hey, this is an HD version of Celestia!Hey, it looks like stars are generated randomly!What?! 3D Landscape and every planet is visitable?!My dream comes true..."

This mean that I liked so much Celestia, i spent a lot of time in it, looking for systems with planets or watching my favourite stars on the pc, then i started to download addons (1,11 GB of addons xD), and i joined the community but after a while they stopped developing, i didn't liked it so much, and i was a bit sad, but when i founded Space Engine, you can't know what i felt

The universe is not required to be in perfect harmony with human ambition.

These screenshots were taken in an "unreleased" build of Celestia (5135)

I've been looking for that build for a while now, but I have not had any luck. (Tried to use the WayBack machine to find leads as well, heck I even went to the source code and compiled it but I got 1.6.0 for my troubles when I grabbed the 1.7 branch.) I'm interested in Celestia specifically because I am interested in modifying it so that it can interact with a modified Linux Distribution.

i remember when i tried this when i was 5 years old before i discovered SE. it was cool.i remember i searched the largest exoplanet there. it was 2005.and today there is much more exoplanets discovered!